The present invention relates to improvements in the outer glass pipes for use with solar heat collector pipes.
Solar heat collector pipes of the type which are designed to protect the outer surface of heat receptor pipes with closed type straight glass pipes are now widely used for solar heat collector equipment. For example, the solar heat collector pipes of vacuum double structure or vacuum single structure have been proposed in the art. The former type collector typically comprises an inner pipe of smaller diameter, having one end closed by rounding and the other end left open, and an outer pipe of larger diameter, having one end closed by rounding and the other end left open, said outer pipe having said inner pipe inserted concentrically therethrough. A space between the outer and inner pipes is then maintained in an air-tight condition under reduced pressure. The latter type collector typically comprises a straight glass pipe having one end closed by rounding, in which a heat medium-filled tube is placed, such as various tubes inclusive of a U-shaped or hair pin tube. A space between the outer pipe and the tube is similarly maintained in an air-tight condition under reduced pressure. In either case, an exhaust glass pipe of a smaller diameter is attached to the closed end of the outer pipe so as to facilitate an air-tight sealing of said space. However, mounting such an exhaust pipe requires, in addition to rounding and other ordinary glass works, drawing, boring which has to be performed by skilled workmen, welding, etc., leading to a considerable rise of the price of product. This is because a series of exhaust pipes are provided in the rounding step involved in the production of outer glass pipes, or separate exhaust pipes are attached to the bottoms of a series of rounded outer pipes as by welding. Additionally, if mishandling occurs in the step of mounting the exhaust pipes on the outer pipes, then the outer pipes should entirely be disposed of, resulting in grave economical losses.
Thus, the prior art glass pipes for solar heat collector pipes of vacuum single or double struction leave much to be desired in view of production and economy inclusive of production cost. Furthermore, the least of mishandling is not permitted in the prior art production system for the foregoing reasons.